Heating device for supplying power to plural heat sources, heating method and image forming apparatus using the heating device

A heating device comprising:

• plural heat sources configured to heat one or more members;
• a power supplying device configured to supply a power to each of the plural heat sources;
• and
• a controller configured to determine a fixed first priority order for the plural heat sources while determining a second priority order for the plural heat sources in every control cycle based on the fixed first priority order and to control the power supplying device to supply a power to one of the plural heat sources according to the second priority order, wherein:
• when the controller judges to activate only one of the plural heat sources in a control cycle, the controller allows the power supplying device to supply a power to one of the plural heat sources in the control cycle,
• when the controller judges to activate two or more of the plural heat sources in a control cycle, the controller allows the power supplying device to supply a power to one of the plural heat sources, which has a highest rank in the second priority order among the two or more of the plural heat sources, in the control cycle, and
• the controller changes the second priority order by according a lowest rank to one of the heat sources activated in a last control cycle while maintaining rank relationship among the others of the plural heat sources in the second priority order in the last control cycle.